The invention is directed to tubes for use as catheter tubes or the like of varying shapes and sizes which are ordinarily employed by medical personnel to drain fluids from body cavities or to distend body passages. It is desirable to know the location of the tube within the body. Elastomeric material such as silicone rubber is extruded to form the tube and simultaneously a silicone X-ray opaque thread is introduced into one wall of the tube as the latter is extruded which readily is exposed when the tube is located in a body and is X-rayed. The method and apparatus produces an extremely effective working catheter tube or the like.